Ethylene oxide is widely used sterilize medical products and fumigate foodstuffs. Although propylene oxide has been suggested as a possible alternative to ethylene oxide, ethylene oxide is still currently the only available method for effectively sterilizing materials that are sensitive to heat, moisture, or radiation.
Approximately 60-70% of industrially sterilized medical devices use ethylene oxide as a sterilant. An estimated 10-12 billion items per year are sterilized with ethylene oxide by manufacturers of medical products. An additional 200-300 million items per year are sterilized with ethylene oxide by hospitals, clinics, physicians, dentists, veterinarians, and research institutions. Almost all of the 18 million surgical procedures performed annually in the United States require the use of items sterilized with ethylene oxide, and many common surgical procedures could not be safely undertaken without ethylene oxide-sterilized equipment.
Unfortunately, ethylene oxide is a suspected human carcinogen with a relatively long atmospheric lifetime of greater than about 100 days. Its background concentration in marine air of the Northern Hemisphere is about 20-50.times.10.sup.-12 liter per liter of air (20-50 parts per trillion by volume-pptv). Concentrations in cities can reach hundreds of pptv. Concentrations up to 3.times.10.sup.-6 (parts per million-ppmv) have been measured near point sources. Moreover, fugitive emissions from manufacturing processes which require large amounts of ethylene oxide, for example the manufacture of ethylene glycol, also release large amounts of this gas into the atmosphere. Most gaseous ethylene oxide used in sterilization and fumigation processes is directly vented to the atmosphere at the present time. Furthermore, prior to the time sterilized items are packaged, they are allowed to sit in "aerators" where residual ethylene oxide diffuses away or outgases from the sterilized items. These sources of gaseous ethylene oxide are difficult to control.
There are four existing control technologies for ethylene oxide emissions: thermal oxidation, catalytic oxidation, acid-catalyzed scrubbing, both with and without solid reactant beds, and condensation/reclamation systems. Although there is a need for a method to remove gaseous ethylene oxide from exhaust gases of sterilizing chambers and other sources, existing methods may not be suitable under certain circumstances. Catalytic oxidation and acid catalyzed scrubbing systems are commercially available for facilities emitting large amounts of ethylene oxide. Ethylene oxide reacts rapidly in acid solution to form ethylene glycol and this is one of the main techniques used to scrub ethylene oxide from exhaust gas streams. However, acid scrubbers and catalytic oxidation units are very expensive. Their average cost is more than $100,000 and they do not scale down easily. The least expensive units are still approximately $50,000. Therefore, it is still extremely expensive for small facilities using ethylene oxide to install scrubbers. These facilities may have to eliminate using ethylene oxide entirely when emission controls become mandatory. Thermal oxidation and condensation/reclamation systems also do not scale down easily for smaller operations.